The present invention relates generally to fan units for scale model airplanes and specifically to ducted fan units for propelling such airplanes.
The prior art inventions have necessitated the use of high rpm engines (racing engines) which require a high nitro fuel. The ducted fan unit structure of the instant invention permits the use of a smaller 0.60 cubic inch, or "standard 0.60 engine" which burns regular airplane fuel to power the scale model. The 0.60 engine is less expensive, easier to tune, and lasts considerably longer than racing engines presently used with fan units of similar size. The use of a smaller engine is permitted in part, by the employment of a larger fan having a different pitch angle in conjunction with the larger cowl and unit overall. In addition, the mounting of the unit within a smooth surface air tunnel extending throughout the plane has facilitated the use of the smaller engine, as has the aerodynamic design of the engine mount. The combination as a whole achieves greater thrust forces at lower rpms than was possible with the prior art inventions.
The present structure is moreover simpler in operation in that the engine is held in an open space which is easily accessible through an opening in the belly of the fuselage. Furthermore, the engine is more easily started in that the fan is turned by the insertion into the fan hub of an extended rod through an opening provided in the tail. Prior art inventions have required a belt to be wrapped around the fan hub for starting.